The use of plant oil is as old as the compression ignition engine itself. Doctor Rudolf Diesel fueled his first engine at the Paris World Exhibition 1990 with 100% peanut oil. In 1911, he stated that The diesel engine can be fed with plant oils and would help considerably in the development of agriculture of the country which is use it. Since his death in 1913, his engine has been modified to run with petroleum fuel because of the huge amount of resource and advancing of refining technology. Recently, because of the ever increasing of petroleum price and quick depletion of fossil fuel resource, especially environment concerns, there has been a renewed focus on the use of biofuels.

Most of countries in ASEAN are still developing, with many rural and remote areas lacking of adequate energy infrastructure. Because of the limitation of transportation, education, and financing, modern fuels and generation systems are often inaccessible to these areas. The use of locally grown plant oils to fuel generation system and provide mechanical power for agriculture becomes the key development for these areas. Many researchers have reported the difficulties with the use of pure plant oils in conventional diesel engine. These problems are mainly attributed to high viscosity of plant oil. There are two strategies for using pure plant oil in conventional diesel

engine: adapt the engine and adapt the fuel. The engine adaptation includes advancing injection timing, increasing injection timing, preheating the oil to reduce viscosity. Viscosity of plant oil can be reduced by blending with diesel, pyrolysis, or make biodiesel via transesterification process. The second strategy needs certain technology that may not be available in rural areas. In this research, three most popular plant oils around ASEAN countries (Palm Oil, Jatropha Oil and Coconut Oil) were selected and tested in a low speed, indirect

injection diesel engine. A preheater was designed using waste heat from engine coolant to reduce viscosity of plant oil. The engine was tuned for improving plant oil combustion. The experimental results reveal that Brake Thermal Efficiency (BTE) is slight higher when the engine is fuelled with plant oil. An improvement in exhaust emissions is also observed at low load. However, as the effect of viscosity becomes dominant as load increases, the combustion process deteriorates and resulting in lower BTE and higher emissions. The results from experiments suggest that selected plant oils could be used as diesel substitution in the near future as far as decentralized energy production is concerned.